A metal mold for resin molding (hereinafter referred to as metal mold), which is used for molding of a thermoplastic resin, is generally given temperature control by heating and cooling depending on the cure temperature of resin to be molded for a product. In this molding, a resin product with better accuracy tends to come out as the temperature of metal mold rises while a melted resin material is supplied into a cavity of the metal mold, since the flowability of melted resin and the transfer of metal mold shape are promoted as the temperature rises. However, when the temperature of metal mold is set to be high, it takes a long period of time to cool down the product as low as it can be accessed to extract, thereby resulting in a problem of time-consuming molding cycle.
A heat exchange apparatus, which is capable of controlling the temperature of a metal mold high and low during molding of a product, has been employed for conventional blow molding and injection molding so that both good transfer of the metal mold shape and a reduction in the molding time cycle can be attained. Examples for this type of heat exchange apparatus are: one which performs heat exchange by supplying hot and cold carriers alternately to a heat exchange passage provided for a metal mold, and the other which employs a heater instead of the hot heat carrier and a cold heat carrier for performing heat exchange.
Though, the conventional heat exchange apparatus, which employs alternate supplying of hot and cold heat carriers, has not yet solved a problem that energy efficiency falls due to the occurrence of a mixture of one heat carrier (e.g. hot heat carrier) remaining in a heat exchange passage and the other heat carrier (e.g. cold heat carrier) supplied anew. On the other hand, the other conventional one with a heater and a cold heat carrier has a problem that the heater unnecessarily supplies heat to the cold heat carrier, which remains in a heat exchange passage, thereby worsening energy efficiency.